Mark date formats as translatable

Fix #1204

src/gui/views/gcal-agenda-view.c

@@ -200,7 +200,13 @@ new_date_header_string (GDateTime *date)
   else if (gcal_date_time_compare_date (date, yesterday) == 0)
     return g_strdup (_("Yesterday"));
   else
-    return g_date_time_format (date, "%A %B %e");
+    /*
+     * Translators: %A is the abbreviated day name, %B is the month name
+     * and %d is the day of the month as a number between 0 and 31.
+     * More formats can be found on the doc:
+     * https://docs.gtk.org/glib/method.DateTime.format.html
+     */
+    return g_date_time_format (date, _("%A %B %d"));
 }